Conventionally, an art is known reducing PM (Particulate matter) included in exhaust gas of a diesel engine with a particulate removing filter referred to as a DPF (Diesel Particulate Filter).
When the temperature of the exhaust gas is higher than regeneration temperature of the DPF, the PM collected in the DPF can be made harmless and removed. On the other hand, when the temperature of the exhaust gas is lower than regeneration temperature of the DPF, the PM collected in the DPF cannot be made harmless and removed. Then, in this case, as regeneration control of the DPF, the temperature of the exhaust gas must be made higher than the regeneration temperature regularly by using EGR and exhaust gas with excessive fuel so as to make the PM collected in the DPF harmless and remove it. For example, the Japanese Patent Laid Open Gazette 2002-276405 discloses the construction in which an inlet throttle valve or an exhaust throttle valve of a diesel engine is throttled so as to raise temperature of exhaust gas, thereby performing regeneration control of a DPF.